Iodine

Endpoint summary

Key value for chemical safety assessment

Toxic effect type:

dose-dependent

Effects on fertility

Description of key information

Key animal testing data are available from an OECD TG 422 study (combined 28-day repeated dose toxicity study with the reproduction/developmental toxicity screening test). The test was conducted in rats orally expoused by oral to iodine. Based on the results of a 10-day dose range finding study, the dose levels for the final study were selected to be 0.3, 3 and 10 mg/kg (initially 30 mg/kg but lowered to 10 mg/kg).

 

No treatment-related changes were noted in any of the reproductive parameters investigated in this study (i.e. mating and fertility indices, precoital time, number of implantations, estrous cycle, spermatogenic profiling, and histopathological examination of reproductive organs) up to the highest dose level tested (10 mg/kg/day). Also, no toxicologically significant changes were noted in any of the developmental parameters investigated in this study (i.e. gestation, viability and lactation indices, duration of gestation, parturition, sex ratio, maternal care and early postnatal pup development consisting of mortality, clinical signs, body weight, and macroscopic examination).

Link to relevant study records

Reference

Endpoint:

screening for reproductive / developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From 2010-02-09 to 2010-05-14

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 422 (Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test)

Version / remarks:

March 1996

Deviations:

no

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

other: Crl:Wl (Han)

Details on species / strain selection:

This species and strain of rat has been recognized as appropriate for general and reproduction toxicity studies. NOTOX BV has general and reproduction/developmental historical data in this species from the same strain and source. This animal model has been proven to be susceptible to the effects of reproductive toxicants.

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, L'Arbresle Cedex, France
- Age at study initiation: Approximately 11 weeks
- Weight at study initiation: Males 329 g ± 20% of the sex mean, Females 192 g ± 20% of the sex mean
- Fasting period before study: Overnight
- Housing:
Pre-mating: Animals were housed in groups of 5 animals/sex/cage in Macrolon cages (MIV type, height 18 cm), except for Female 81 which was single housed.
Mating: Females were caged together with males on a one-to-one-basis in Macrolon cages (MIII type, height 18 cm).
Post-mating: Males were housed in their home cage (Macrolon cages, MIV type, height 18 cm) with a maximum of 5 animals/cage. Females were individually housed in Macrolon cages (MIII type, height 18 cm).
Lactation: Pups were kept with the dam until termination in Macrolon cages (MIII type, height 18 cm).
- Diet (e.g. ad libitum): Free access to pelleted rodent diet (SM R/M-Z from SSNIFF® Spezialdiäten GmbH, Soest, Germany)
- Water (e.g. ad libitum): Free access to tap-water.
- Acclimation period: At least 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21.0 ± 3.0
- Humidity (%): 40-70
- Air changes (per hr): 15
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

oral: gavage

Vehicle:

DMSO

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
Formulations of Group 4 and/or a stock solution (w/w) were prepared daily within 6 hours prior to dosing and were homogenised to a visually acceptable level. Adjustment was made for specific gravity of the vehicle. The Group 2 and 3 formulations were prepared by dilution of the Group 4 formulation or the stock solution. Solutions were stored at ambient temperature.

VEHICLE
- Justification for use and choice of vehicle: Dimethyl sulphoxide (DMSO), specific gravity 1.1 (Merck, Darmstadt, Germany). DMSO was selected based on trial formulations performed at NOTOX.
- Amount of vehicle (if gavage): 1 mL/kg body weight. Actual dose volumes were calculated according to the latest body weight. This dose volume was based on results of a 13 week oral study in the rat in which a NOEL of 1100 mg/kg body weight/day was established (information from MSDS).

Details on mating procedure:

- M/F ratio per cage: one female/one male
- Length of cohabitation: 14 days (maximum)
- Proof of pregnancy: vaginal plug or sperm in vaginal smear referred to as day 0 post-coitum
- Further matings after two unsuccessful attempts: no
- After successful mating each pregnant female was caged (how): Males were housed in their home cage with a maximum of 5 animals/cage. Females were individually housed in Macrolon cages.
- Any other deviations from standard protocol: Mating of female no. 50 was overlooked, since live offspring was delivered by this animal.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analyses were conducted on a single occasion during the treatment phase (24 March 2010), according to a validated method (NOTOX project 492834). Samples of formulations were analyzed for homogeneity (highest* and lowest concentration) and accuracy of preparation (all concentrations). Stability in vehicle over 6 hours at room temperature under protection from light and stability over 7 days in a refrigerator was also determined for the highest* and lowest concentrations.

*The highest concentration was 30 mg/mL (analyses were performed before change to 10 mg/mL).

Duration of treatment / exposure:

Males were exposed for 29 days, ie. 2 weeks prior to mating, during mating, and up to termination. Females were exposed for 41-47 days, i.e. during 2 weeks prior to mating, during mating, during post-coitum, and during at least 4 days of lactation.

Frequency of treatment:

Once daily

Details on study schedule:

- Age at mating of the mated animals in the study: 13 weeks

Dose / conc.:

10 mg/kg bw/day (actual dose received)

Remarks:

Animals were dosed 30 mg/kg bw/day for 4 days but because of clinical signs, the dose level was lowered to 10 mg/kg bw/day.

Dose / conc.:

3 mg/kg bw/day (actual dose received)

Dose / conc.:

0.3 mg/kg bw/day (actual dose received)

No. of animals per sex per dose:

10 animals/sex/group

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: In order to set the dose levels for the main study, a dose range finding study was performed. Groups of 3 females (11-13 weeks old) were dosed at 1, 10 or 100 mg/kg/day for 10 days by oral gavage. At 1 and 10 mg/kg no toxicologically significant toxicity was noted. Animals treated at 100 mg/kg from Day 2 onwards showed clinical signs consisted of lethargy, hunched posture, piloerection, lean appearance, and/or rales. All three female rats were killed in extremis on Day 4 of treatment.
- Rationale for animal assignment (if not random): by computer-generated random algorithm according to body weight, with all animals within ± 20% of the sex mean.

Positive control:

No

Parental animals: Observations and examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: At least twice daily.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Immediately after each dosing, once prior to start of treatment and at weekly intervals.

BODY WEIGHT: Yes
- Time schedule for examinations: Males and females were weighed on the first day of exposure and weekly thereafter. Mated females were weighed on days 0, 4, 7, 11, 14, 17 and 20 post-coitum, and during lactation on days 1 and 4.

FOOD CONSUMPTION AND COMPOUND INTAKE
- Time schedule for examinations: Weekly, except for males and females which were housed together for mating and for females without evidence of mating. Food consumption of mated females was measured on Days 0, 4, 7, 11, 14, 17 and 20 post-coitum and on Days 1 and 4 of lactation.

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No

WATER CONSUMPTION AND COMPOUND INTAKE: Yes, Subjective appraisal was maintained during the study, but no quantitative investigation was introduced as no effect was suspected.

FUNCTIONAL OBSERVATIONS
Hearing ability, pupillary reflex, static righting reflex, grip strength tests were performed on the selected 5 animals/sex/group.
The selected males were tested during Week 4 of treatment and the selected females were tested towards the end of the scheduled lactation period (all before blood sampling). In order to avoid hypothermia of pups, dams were removed from the pups for not more than 30-40 minutes.

LOCOMOTOR ACTIVITY
The motor activity test (recording period: 1-hour for individual animals, using a computerised monitoring system, Pearson Technical Services, Suffolk, Great Britain) was performed on the 5 selected animals/sex/group.
During the motor activity test, males were caged individually and females were caged with their pups.
The selected males were tested during Week 4 of treatment and the selected females were tested during lactation (all before blood sampling).

GENERAL REPRODUCTION DATA
Male number paired with, mating date, confirmation of pregnancy, and delivery day were recorded. Pregnant females were examined to detect signs of difficult or prolonged parturition, and cage debris of these females was examined to detect signs of abortion or premature birth. Any deficiencies in maternal care (such as inadequate construction or cleaning of the nest, pups left scattered and cold, physical abuse of pups or apparently inadequate lactation or feeding) were examined.

Oestrous cyclicity (parental animals):

No data

Sperm parameters (parental animals):

Parameters examined in male parental generation:
testis weight and epididymis weight

Litter observations:

PARAMETERS EXAMINED
The following parameters were examined in offspring:
number and sex of pups (day 1 and 4 of lactation), viability (daily), body weights (day 1 and 4 of lactation), clinical signs (daily).
Necropsy: Pups surviving to planned termination were killed by decapitation on lactation Day 5, 6 or 7. All pups were sexed and descriptions of all external abnormalities were recorded. The stomach was examined for the presence of milk.

GROSS EXAMINATION OF DEAD PUPS:
yes, for external abnormalities

Postmortem examinations (parental animals):

SACRIFICE
- Male animals: All surviving animals following completion of the mating period (a minimum of 28 days of dose administration).
- Maternal animals: All surviving animals at lactation Days 5-7; Females which were non pregnant (No 46 and No 56) at post-coitum Day 26 (females with evidence of mating)

GROSS NECROPSY
- Gross necropsy consisted of external and internal examinations including the cervical, thoracic, and abdominal viscera.

HISTOPATHOLOGY / ORGAN WEIGHTS
The tissues indicated in Table 1 were prepared for microscopic examination and weighed Table 2.

Postmortem examinations (offspring):

SACRIFICE
- The offspring were sacrificed on lactation Day 5, 6 or 7.
- These animals were subjected to postmortem examinations macroscopic as follows

GROSS NECROPSY
- Gross necropsy consisted of external aexaminations. The stomach was examined for the presence of milk

Statistics:

- If the variables could be assumed to follow a normal distribution, the Dunnett-test based on a pooled variance estimate was applied for the comparison of the treated groups and the control groups for each sex.
- The Steel-test was applied if the data could not be assumed to follow a normal distribution.
- The Fisher Exact-test was applied to frequency data.
The following additional methods of statistical analysis were used:
The number of corpora lutea was transformed by using 1/x to obtain a normal distribution. This was followed by an ANOVA. The Dunnett-test (many-to-one t-test) based on a pooled variance estimate was applied for the comparison of the treated groups and the control group.
All tests were two-sided and in all cases p < 0.05 was accepted as the lowest level of significance.

Reproductive indices:

Mating (%): Number of females mated/Number of females paired x 100
Fertility index (%): Number of pregnant females/Number of females paired x 100
Conception index (%): Number of pregnant females/Number of females mated x 100
Gestation index (%): Number of females bearing live pups/Number of pregnant females x 100
Duration of gestation: Number of days between confirmation of mating and the biginning of parturition

Offspring viability indices:

Percentage live males at first litter check: Number of live male pups at first litter check/Number of live pups at first litter check x 100
Percentage live females at first litter check: Number of live female pups at first litter check/Number of live pups at first litter check x 100
Percentage of postnatal loss days 0-4 of lactation: Number of dead pups on day 4 of lactation/Number of live pups at first litter check x 100
Viability index (%): Number of live pups on day 4 of lactation/Number of pups born alive x 100

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Haematological findings:

effects observed, non-treatment-related

Clinical biochemistry findings:

effects observed, non-treatment-related

Behaviour (functional findings):

effects observed, non-treatment-related

Organ weight findings including organ / body weight ratios:

effects observed, non-treatment-related

Histopathological findings: non-neoplastic:

no effects observed

Reproductive function: oestrous cycle:

not examined

Reproductive function: sperm measures:

not examined

Reproductive performance:

no effects observed

CLINICAL SIGNS AND MORTALITY (PARENTAL ANIMALS)

One female at 30 mg/kg Group 4, Female no.80) was killed in extremis on Day 2 of the treatment period.
This animal showed hunched posture, piloerection, ptosis and pale appearance, and a body weight loss of 10% over one day. At necropsy, many dark red foci on the thymus were noted and reddish discoloration of the gastro-intestinal tract that was also distended with gas. At microscopic examination, this animal had minimal to severe degrees of villous atrophy in the duodenum, jejunum and cecum along with moderate atrophy of the gastric mucosa. These findings indicate a functional disturbance of the gastrointestinal tract which was considered to have contributed to moribundity in this animal. As this animal had been dosed at 30 mg/kg which resulted in a 10% loss of body weight within 24 hours, a relationship to treatment cannot be excluded.

Clinical signs of toxicity were noted at 30 mg/kg for females. No treatment related clinical signs were noted up to 10 mg/kg.
At 30 mg/kg, hunched posture, piloerection, pale appearance and ptosis were noted for female no. 80 on the day she was euthanized in extremis (Day 2 of treatment). In addition, Female 75 showed hunched posture on Days 3-5 of treatment. This was considered to have been caused
by treatment at 30 mg/kg on Days 1-3 (not from treatment at 10 mg/kg which she received from Day 4 onwards).

Redness and swelling of both ears was noted for female no. 79 (Group 4, 10 mg/kg) over the repro period. Microscopic examination revealed slight unilateral lymphohistiocytic inflammation with cartilage necrosis. At this single incidence it was considered to have occurred by chance
and not to be treatment related.
Incidental findings that were noted included scabs and alopecia. These findings occurred within the range of background findings to be expected for rats of this age and strain which are housed and treated under the conditions in this study.

Partly based on these findings, the dose level of Group 4 was lowered on Day 4 of the treatment period from 30 mg/kg to 10 mg/kg.

BODY WEIGHT AND FOOD CONSUMPTION (PARENTAL ANIMALS)

Body weights and body weight gain of treated animals remained in the same range as controls over the treatment period up to 10 mg/kg.
At 30 mg/kg, body weight loss was noted for five out of ten females (range of 1-12% body weight loss in two days).
Partly based on these findings, the dose level of Group 4 was lowered on Day 4 of the treatment period from 30 mg/kg to 10 mg/kg.

Food consumption before or after allowance for body weight was similar between treated and control animals.
Food consumption was slightly reduced for the first week for females of Group 4 (cages 15-16; not statistically significant). This was considered to have been caused by the high dose level of 30 mg/kg given for the first three days of dosing.

TEST SUBSTANCE INTAKE (PARENTAL ANIMALS)

Not examined (gavage study)

REPRODUCTIVE FUNCTION: ESTROUS CYCLE (PARENTAL ANIMALS)

Not examined

REPRODUCTIVE FUNCTION: SPERM MEASURES (PARENTAL ANIMALS)

Not examined

REPRODUCTIVE PERFORMANCE (PARENTAL ANIMALS)

No toxicologically relevant effects on reproductive parameters were noted.
Mating, fertility and conception index, precoital time, and number of corpora lutea and implantation sites were unaffected by treatment.
The statistically significantly increased number of implantation sites noted for low dose females (0.3 mg/kg) was not considered toxicologically relevant, as no dose response was seen and values were within normal limits.

ORGAN WEIGHTS (PARENTAL ANIMALS)

No toxicologically relevant changes were noted in organ weights and organ to body weight ratios.
At 10 mg/kg (Group 4), the higher liver to body weight ratio seen for males was not reflective of treatment related toxicity because the mean and individual values remained well within the range of data considered normal for this age and strain and no microscopic correlate was noted.
Two females treated at 10 mg/kg (nos. 73 and 75) showed relatively high thymus weights when compared to the concurrent control values. However, these values were still within normal limits and in the absence of microscopic findings, were not regarded toxicologically relevant.
Other organ weights and organ to body weight ratios among the dose groups were similar to control levels.

GROSS PATHOLOGY (PARENTAL ANIMALS)

Necropsy did not reveal any toxicologically relevant alterations up to 10 mg/kg.
At 30 mg/kg, the female that was euthanized in extremis (no. 80) was noted with many dark red foci on the thymus and reddish discoloration of the gastro-intestinal tract that was also distended with gas.
Incidental findings included dark red discoloration of the mandibular lymph nodes, black discoloration of the popliteal lymph nodes, an isolated red focus or many dark red foci on the thymus, soft yellow nodule on the tail and body of the left epididymide, thickening of the ears, pelvic dilation of the kidneys, and alopecia over various body regions. The incidence of these findings was within the background range of findings that are encountered among rats of this age and strain, and did not show a dose-related incidence trend. These necropsy findings were therefore not considered to be toxicologically relevant.

HISTOPATHOLOGY (PARENTAL ANIMALS)

There were no treatment-related microscopic findings.
One female Group 4 animal (30 mg/kg, animal 80) was sacrificed moribund after one day on test. This animal had minimal to severe degrees of villous atrophy in the duodenum, jejunum and cecum along with moderate atrophy of the gastric mucosa. These findings indicate a functional disturbance of the gastrointestinal tract which was considered to have contributed to moribundity in this animal. As this animal had been dosed at 30 mg/kg which resulted in a 10% loss of bodyweight within 24 hours, a relationship to treatment cannot be excluded.
No abnormalities were seen in the reproductive organs of the suspected non-fertile animals (Group 1 female 46 and male 6 and Group 2 female 56 and male 16) which could account for their infertility.
All microscopic findings recorded were considered to be within the normal range of background pathology encountered in Wistar-Han rats of this age and strain.

FUNCTIONAL OBSERVATIONS
No toxicologically relevant effects on hearing ability, pupillary reflex, static righting reflex and grip strength were observed.
One female treated at 0.3 mg/kg (Group 2, no. 54) showed absent grip strength. As it concerning only one animal of the low dose group, it was not considered toxicologically relevant.
The variation in motor activity did not indicate a relation with treatment. Females at 10 mg/kg (Group 4) had higher activity counts (low sensor; not statistically significant). As the values were well within normal limits and it occurred in the absence of any corroborative findings like hyperactivity, the increase was not considered to be toxicologically relevant.

Dose descriptor:

NOAEL

Effect level:

10 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

gross pathology

neuropathology

reproductive performance

Critical effects observed:

no

Clinical signs:

effects observed, non-treatment-related

Mortality / viability:

mortality observed, non-treatment-related

Body weight and weight changes:

no effects observed

Sexual maturation:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

effects observed, non-treatment-related

Histopathological findings:

not examined

VIABILITY (OFFSPRING)

The gestation index and duration of gestation were similar between controls and all treated groups. Number of dead and living pups at first litter check, postnatal loss, viability index and sex ratio were unaffected by treatment

CLINICAL SIGNS (OFFSPRING)

Incidental clinical symptoms of pups consisted of small size, scabbing of the abdomen and pale appearance were noted. The nature and incidence of these clinical signs remained within the range considered normal for pups of this age, and were therefore considered to be of no toxicological relevance.

BODY WEIGHT (OFFSPRING)

Body weights of pups were considered to have been unaffected by treatment.

SEXUAL MATURATION (OFFSPRING)

Not examined

ORGAN WEIGHTS (OFFSPRING)

Not examined

GROSS PATHOLOGY (OFFSPRING)

The incidental macroscopic finding of small size was noted for one pup. The nature and incidence of these findings remained within the range considered normal for pups of this age, and was therefore not considered to be toxicologically relevant.

HISTOPATHOLOGY (OFFSPRING)

Not examined

MORTALITY

One pup of the control group, three pups at 3 mg/kg and two pups at 10 mg/kg were missing during Days 2-4 of lactation. No toxicological relevance was attributed to these missing pups since the mortality incidence did not show a dose-related trend and remained within the range considered normal for pups of this age. Missing pups were most likely cannibalised.

PARTURITION/MATERNAL CARE
No signs of difficult or prolonged parturition were noted among the pregnant females.
Examination of cage debris of pregnant females revealed no signs of abortion or premature birth. No deficiencies in maternal care were observed.

EARLY POSTNATAL PUP DEVELOPMENT

Number of dead and living pups at first litter check, postnatal loss, viability index and sex ratio were unaffected by treatment, and clinical signs, body weight and external macroscopy did not reveal treatment-related findings.

Dose descriptor:

NOAEL

Generation:

F1

Effect level:

10 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

gross pathology

Reproductive effects observed:

no

Analysis of Dose Preparations

The concentrations analysed in the formulations of Group 2 (0.273 mg/g), Group 3 (2.73 mg/g) and Group 4 (27.3 mg/g) were in agreement with target concentrations (i.e. mean accuracies between 90% and 110%). No test substance was detected in the Group 1 formulations.

The formulations of Group 2 and Group 4 were homogeneous (i.e. coefficient of variation ≤ 10%).

Formulations at the highest concentration level (i.e. 27.3 mg/g) were stable when stored in a refrigerator for at least 7 days. Formulations at the lowest concentration level (i.e. 0.273 mg/g) were stable when stored at room temperature for at least 6 hours, but not stable when stored in a refrigerator for 7 days.

Conclusions:

A combined 28-day repeated dose toxicity study with the reproduction/developmental toxicity screening test was conducted with Iodine in rats by oral gavage following OECD 422.

Based on the results, a reproduction and developmental No Observed Adverse Effect Level (NOAEL) of 10 mg/kg was derived

Executive summary:

A combined 28-day repeated dose toxicity study with the reproduction/developmental toxicity screening test was conducted with Iodine in rats by oral gavage following OECD 422.

 

Based on the results of a 10-day dose range finding study, the dose levels for this combined 28-day oral gavage study with reproduction/developmental toxicity screening test were selected to be 0.3, 3 and 30 mg/kg.

 

After acclimatisation, four groups of ten male and ten female Wistar Han rats were exposed by oral gavage to the test substance at 0, 0.3, 3 and 30 mg/kg. Due to severe toxicity at 30 mg/kg, the dose level of Group 4 was adjusted to 10 mg/kg from Day 4 of the study onwards. Males were exposed for 29 days, i.e. 2 weeks prior to mating, during mating, and up to termination. Females were exposed for 41-47 days, i.e. during 2 weeks prior to mating, during mating, during post-coitum, and during at least 4 days of lactation.

 

The following parameters were evaluated in the parental animals: mortality/viability, clinical signs, functional observations, body weights, food consumption, reproduction/developmental parameters, observations pups, clinical pathology (including thyroid hormones), macroscopy, organ weights, and histopathology. Pups were examined for viability, clinical signs, and body weights were determined. All pups were sexed and descriptions of all external abnormalities were recorded at necropsy. Chemical analyses of formulations were conducted once during the study to assess accuracy, homogeneity and stability.

No reproductive toxicity was observed up to the highest dose level tested (10 mg/kg/day). No treatment-related changes were noted in any of the reproductive parameters investigated in this study (i.e. mating and fertility indices, precoital time, number of implantations, estrous cycle, spermatogenic profiling, and histopathological examination of reproductive organs).

No developmental toxicity was observed up to the highest dose level tested (10 mg/kg/day). No toxicologically significant changes were noted in any of the developmental parameters investigated in this study (i.e. gestation, viability and lactation indices, duration of gestation, parturition, sex ratio, maternal care and early postnatal pup development consisting of mortality, clinical signs, body weight, and macroscopic examination).

 

Based on the results of this combined 28-day repeated dose toxicity study with the reproduction/developmental toxicity screening test, the no-observed-adverse-effect levels (NOAEL) for reproduction and developmental toxicity was evaluated to be 10 mg/kg bw/day.

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

10 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Quality of whole database:

Animal data available including an OCD 422 study identified as the key study.
Human data available from expert opinions, thesedata ar described below, and further in section 7.10.

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

Other animal data reported in section 7.8.1. but conisdered less relevant :

In the following, a number of the most relevant supportive animal data are described:

- Arrington, 1965 conducted a series of experiments was with Dutch and New Zealand rabbits, Syrian hamsters, Long-Evans rats and Hampshire-Duroc crossbred swine. Two-hundred and fifty to 1000 ppm iodine fed for 2 to 5 days caused increasing mortality of newborn rabbits. Hamsters were not affected by 2500 ppm iodine except for slightly reduced feed intake and decreased weaning weight of the young. Gestation time for rats was not affected by 2500 ppm iodine; however, prolonged parturition was observed in rats. Swine were not affected by dietary levels of iodine at 1500 or 2500 ppm.

- Ammermann, 1964 conducted a series of experiments in which adult female rats were fed zero to 2500 ppm supplemental iodine from zero to approximately 35 days prepartum. Increasing mortality of young after birth occurred with increasing levels of iodine.

- Mahapatra, 2017 investigate the effect of excess iodine on the ovarian physiology. Prolonged exposure of iodine in excess exerts biphasic mode of action depending on the dose in female reproductive physiology and both the doses used in this study affected fertility equally.

- Chakraborty, 2016 evaluate the effect of prolonged increased iodine intake in adult male reproductive physiology. Overall results revealed that regular consumption of iodine in excess impairs reproductive functions in adult male rats depending on the dose and duration of its exposure through different mechanisms.

Human data (from expert opinions):

The effects of iodine on human reproduction are well known from literature data. Exposure to excess iodine may produce hypothyroidism or hyperthyroidism and could cause disruption of reproductive function, secondary to thyroid gland dysfunction. Hypothyroidism can produce changes in the menstrual cycle in humans, including menorrhagia (excessive uterine bleeding) and anovulation (no ovulation). Spontaneous abortions, stillbirths, and premature births have also been associated with hypothyroidism. Reproductive impairments associated with hyperthyroidism include amenorrhea and alterations in gonadotropin release and sex hormone-binding globulin (SHBG), and associated changes in the levels and metabolism of steroid hormones in both females and males (ATSDR, 2004).

WHO (2020) also discusses effects of iodine on human reproduction with the follwing observations:

"Chronic exposure to excess iodine has been shown to disrupt reproductive function, as a result of thyroid gland dysfunction. Changes in the menstrual cycle, including menorrhagia (excessive uterine bleeding) and anovulation (no ovulation), spontaneous abortions, stillbirths and premature births have been associated with hypothyroidism (Longcope, 2000a; Krassas, Poppe & Glinoer, 2010). Reproductive impairments associated with hyperthyroidism include amenorrhea (absence of menstruation), alterations in gonadotrophin-releasing hormone and sex hormone-binding globulin, and changes in the levels and metabolism of steroid hormones in both females and males (Longcope, 2000b; Krassas, Poppe & Glinoer, 2010)".

Summary:

The effects of iodine on human reproduction are well known from literature data. Exposure to excess iodine may produce hypothyroidism or hyperthyroidism and could cause disruption of reproductive function, secondary to thyroid gland dysfunction. As human data is availabele, data on experimental animals are considered secondary to human data in the assessment for effets on fertility and development.

Key references:

- Agency for Toxic Substances and Disease Registry (ATSDR). 2004. Toxicological profile for iodine.

- World Health Organization (WHO). 2009. Iodine and inorganic iodides. In: Concise International Chemical Assessment Document 72.

- WHO, 2020: Iodin in drinking water, Background document for development of WHO guidelines for drinking-water quality.

Effects on developmental toxicity

Description of key information

Key animal testing data are available from an OECD TG 422 study(combined 28-day repeated dose toxicity study with the reproduction/developmental toxicity screening test). The test was conducted in rats orally expoused by oral to iodine. Based on the results of a 10-day dose range finding study, the dose levels for the final study were selected to be 0.3, 3 and 10 mg/kg (initially 30 mg/kg but lowered to 10 mg/kg).

No treatment-related changes were noted in any of the reproductive parameters investigated in this study (i.e. mating and fertility indices, precoital time, number of implantations, estrous cycle, spermatogenic profiling, and histopathological examination of reproductive organs) up to the highest dose level tested (10 mg/kg/day). Also, no toxicologically significant changes were noted in any of the developmental parameters investigated in this study (i.e. gestation, viability and lactation indices, duration of gestation, parturition, sex ratio, maternal care and early postnatal pup development consisting of mortality, clinical signs, body weight, and macroscopic examination).

Further key data are available from Yang (2006). Balb/C mice were given different doses of iodine at the levels of 0 (sterile water), 1500, 3000, 6000, 12,000 and 24,000 µg/L in drinking water for 4 months, then were mated and the developmental toxicity and teratogenicity were evaluated.

Serum total thyroxine (TT4) levels increased and serum total triiodothyronine (TT3) levels decreased significantly in dams when iodine dose reached 3000 µg/L. Maternal effect was evident by the reduction of average daily food consumption in higher doses of iodine groups. Embryotoxicity and teratogenicity were mainly indicated by the reduced body weight in female fetuses, the decreased number of live fetuses, and the increased incidence of resorptions, and especially skeletal variations.

Based on study results, embryotoxicity and teratogenicity were mainly indicated by the reduced body weight in female fetuses, the decreased number of live fetuses, and the increased incidence of resorptions, and especially skeletal variations. A NOAEL for fetotoxicity could not be obtained. Fetotoxicity LOAEL was 1500 µg/L.

Link to relevant study records

Reference

Reference 1

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: OECD guideline study following GLPs

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 422 (Combined repeated dose toxicity study with the reproduction/developmental toxicity screening test, 2002) and US EPA Guideline OPPTS 870.3650 (2000)

Deviations:

yes

Remarks:

The study integrity was not adversely affected by the deviations

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

other: Crl:Wl (Han)

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, L'Arbresle Cedex, France
- Age at study initiation: Approximately 11 weeks
- Weight at study initiation: Males 329 g ± 20% of the sex mean, Females 192 g ± 20% of the sex mean
- Fasting period before study: Overnight
- Housing:
Pre-mating: Animals were housed in groups of 5 animals/sex/cage in Macrolon cages (MIV type, height 18 cm), except for Female 81 which was single housed.
Mating: Females were caged together with males on a one-to-one-basis in Macrolon cages (MIII type, height 18 cm).
Post-mating: Males were housed in their home cage (Macrolon cages, MIV type, height 18 cm) with a maximum of 5 animals/cage. Females were individually housed in Macrolon cages (MIII type, height 18 cm).
Lactation: Pups were kept with the dam until termination in Macrolon cages (MIII type, height 18 cm).
- Diet (e.g. ad libitum): Free access to pelleted rodent diet (SM R/M-Z from SSNIFF® Spezialdiäten GmbH, Soest, Germany)
- Water (e.g. ad libitum): Free access to tap-water.
- Acclimation period: 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21.0 ± 3.0
- Humidity (%): 40-70
- Air changes (per hr): 15
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

oral: gavage

Vehicle:

DMSO

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
Formulations of Group 4 and/or a stock solution (w/w) were prepared daily within 6 hours prior to dosing and were homogenised to a visually acceptable level. Adjustment was made for specific gravity of the vehicle. The Group 2 and 3 formulations were prepared by dilution of the Group 4 formulation or the stock solution. Solutions were stored at ambient temperature.

VEHICLE
- Justification for use and choice of vehicle: Dimethyl sulphoxide (DMSO), specific gravity 1.1 (Merck, Darmstadt, Germany). DMSO was selected based on trial formulations performed at NOTOX.
- Amount of vehicle (if gavage): 1 mL/kg body weight. Actual dose volumes were calculated according to the latest body weight. This dose volume was based on results of a 13 week oral study in the rat in which a NOEL of 1100 mg/kg body weight/day was established (information from MSDS).

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analyses were conducted on a single occasion during the treatment phase (24 March 2010), according to a validated method (NOTOX project 492834). Samples of formulations were analyzed for homogeneity (highest* and lowest concentration) and accuracy of preparation (all concentrations). Stability in vehicle over 6 hours at room temperature under protection from light and stability over 7 days in a refrigerator was also determined for the highest* and lowest concentrations.

*The highest concentration was 30 mg/mL (analyses were performed before change to 10 mg/mL).

Details on mating procedure:

- Impregnation procedure: cohoused
- If cohoused:
- M/F ratio per cage: one female/one male
- Length of cohabitation: 14 days
- Proof of pregnancy: vaginal plug or sperm in vaginal smear referred to as day 0 post-coitum
- Further matings after two unsuccessful attempts: no
- After successful mating each pregnant female was caged (how): Males were housed in their home cage with a maximum of 5 animals/cage. Females were individually housed in Macrolon cages.
- Any other deviations from standard protocol: Mating of female no. 50 was overlooked, since live offspring was delivered by this animal.

Duration of treatment / exposure:

Males were exposed for 29 days, ie. 2 weeks prior to mating, during mating, and up to termination. Females were exposed for 41-47 days, i.e. during 2 weeks prior to mating, during mating, during post-coitum, and during at least 4 days of lactation.

Frequency of treatment:

Once daily

Duration of test:

Parental males were necropsied at completion of mating period (minimum 28 days of treatment), females which delivered were necropsied in lactation days 5-7. Non-pregnant females were necropsied in day 26 post-coitum. Pups were examined (necropsied) in lactation days 5-7.

Remarks:

Doses / Concentrations:
10 mg/kg bw/day
Basis:
actual ingested

Remarks:

Doses / Concentrations:
3 mg/kg bw/day
Basis:
actual ingested

Remarks:

Doses / Concentrations:
0.3 mg/kg bw/day
Basis:
actual ingested

No. of animals per sex per dose:

10 animals/sex/group

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: In order to set the dose levels for the main study, a dose range finding study was performed. Groups of 3 females (11-13 weeks old) were dosed at 1, 10 or 100 mg/kg/day for 10 days by oral gavage. At 1 and 10 mg/kg no toxicologically significant toxicity was noted. Animals treated at 100 mg/kg from Day 2 onwards showed clinical signs consisted of lethargy, hunched posture, piloerection, lean appearance, and/or rales. All three female rats were killed in extremis on Day 4 of treatment.
- Rationale for animal assignment (if not random): by computer-generated random algorithm according to body weight, with all animals within ± 20% of the sex mean.

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Twice daily.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Immediately after each dosing, once prior to start of treatment and at weekly intervals.

BODY WEIGHT: Yes
- Time schedule for examinations: Males and females were weighed on the first day of exposure and weekly thereafter. Mated females were weighed on days 0, 4, 7, 11, 14, 17 and 20 post-coitum, and during lactation on days 1 and 4.

FOOD CONSUMPTION AND COMPOUND INTAKE
- Time schedule for examinations: Weekly, except for males and females which were housed together for mating and for females without evidence of mating. Food consumption of mated females was measured on Days 0, 4, 7, 11, 14, 17 and 20 post-coitum and on Days 1 and 4 of lactation.


WATER CONSUMPTION AND COMPOUND INTAKE: Yes, Subjective appraisal was maintained during the study, but no quantitative investigation was introduced as no effect was suspected.

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day: Parental males were necropsied at completion of mating period (minimum 28 days of treatment), females which delivered were necropsied in lactation days 5-7. Non-pregnant females were necropsied in day 26 post-coitum
- Organs examined: Table 1 and Table 2

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: No
- Number of corpora lutea: Yes
- Number of implantations: Yes
- Number of early resorptions: No data
- Number of late resorptions: No data

Fetal examinations:

- External examinations: Yes: all per litter
- Soft tissue examinations: No
- Skeletal examinations: No
- Head examinations: No

Statistics:

- If the variables could be assumed to follow a normal distribution, the Dunnett-test based on a pooled variance estimate was applied for the comparison of the treated groups and the control groups for each sex.
- The Steel-test was applied if the data could not be assumed to follow a normal distribution.
- The Fisher Exact-test was applied to frequency data.
The following additional methods of statistical analysis were used:
The number of corpora lutea was transformed by using 1/x to obtain a normal distribution. This was followed by an ANOVA. The Dunnett-test (many-to-one t-test) based on a pooled variance estimate was applied for the comparison of the treated groups and the control group.
All tests were two-sided and in all cases p < 0.05 was accepted as the lowest level of significance.

Indices:

Percentage live males at first litter check: Number of live male pups at first litter check/Number of live pups at first litter check x 100
Percentage live females at first litter check: Number of live female pups at first litter check/Number of live pups at first litter check x 100
Percentage of postnatal loss days 0-4 of lactation: Number of dead pups on day 4 of lactation/Number of live pups at first litter check x 100
Viability index (%): Number of live pups on day 4 of lactation/Number of pups born alive x 100

Historical control data:

No data

Details on maternal toxic effects:

Maternal toxic effects:no effects

Details on maternal toxic effects:
No toxicologically relevant effects on gestation index and duration, parturition, maternal care and early postnatal pup development (mortality, clinical signs, body weight and macroscopy) were observed.
Gestation
The gestation index and duration of gestation were similar between controls and all treated groups.

Parturition/Maternal care
No signs of difficult or prolonged parturition were noted among the pregnant females. Examination of cage debris of pregnant females revealed no signs of abortion or premature birth. No deficiencies in maternal care were observed.

Early postnatal pup development
Number of dead and living pups at first litter check, postnatal loss, viability index and sex ratio were unaffected by treatment, and clinical signs, body weight and external macroscopy did not reveal treatment-related findings.

Mortality
One pup of the control group, three pups at 3 mg/kg and two pups at 10 mg/kg were missing during Days 2-4 of lactation. No toxicological relevance was attributed to these missing pups since the mortality incidence did not show a dose-related trend and remained within the range considered normal for pups of this age. Missing pups were most likely cannibalised.

Clinical signs
Incidental clinical symptoms of pups consisted of small size, scabbing of the abdomen and pale appearance were noted. The nature and incidence of these clinical signs remained within the range considered normal for pups of this age, and were therefore considered to be of no toxicological relevance.

Body weights
Body weights of pups were considered to have been unaffected by treatment.

Macroscopy
The incidental macroscopic finding of small size was noted for one pup. The nature and incidence of these findings remained within the range considered normal for pups of this age, and was therefore not considered to be toxicologically relevant.

Dose descriptor:

NOAEL

Effect level:

10 mg/kg bw/day (actual dose received)

Based on:

test mat.

Basis for effect level:

other: developmental toxicity

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:no effects

Dose descriptor:

NOAEL

Effect level:

10 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

changes in postnatal survival

external malformations

Abnormalities:

not specified

Developmental effects observed:

not specified

Analysis of Dose Preparations

The concentrations analysed in the formulations of Group 2 (0.273 mg/g), Group 3 (2.73 mg/g) and Group 4 (27.3 mg/g) were in agreement with target concentrations (i.e. mean accuracies between 90% and 110%). No test substance was detected in the Group 1 formulations.

The formulations of Group 2 and Group 4 were homogeneous (i.e. coefficient of variation ≤ 10%).

Formulations at the highest concentration level (i.e. 27.3 mg/g) were stable when stored in a refrigerator for at least 7 days. Formulations at the lowest concentration level (i.e. 0.273 mg/g) were stable when stored at room temperature for at least 6 hours, but not stable when stored in a refrigerator for 7 days.

Conclusions:

No reproduction/developmental toxicity was observed at any dose level. Based on these results, a reproduction and developmental No Observed Adverse Effect Level. (NOAEL) of 10 mg/kg was derived.

Executive summary:

A combined 28-day repeated dose toxicity study with the reproduction/developmental toxicity screening test was conducted with Iodine in rats by oral gavage.

The study was based following guidelines from Organisation of Economic Co-operation and Development Guidelines (OECD) for testing of Chemicals Guideline 422, Combined Repeated Dose Toxicity Study with the Reproduction/Developmental Toxicity Screening Test (1996) and The United States Environmental Protection Agency (EPA) Health Effects Test Guidelines OPPTS 870.3650, Combined Repeated Dose Toxicity Study with the Reproduction/Developmental Toxicity Screening Test (2000).

Based on the results of a 10-day dose range finding study, the dose levels for this combined 28-day oral gavage study with reproduction/developmental toxicity screening test were selected to be 0.3, 3 and 30 mg/kg.

After acclimatisation, four groups of ten male and ten female Wistar Han rats were exposed by oral gavage to the test substance at 0, 0.3, 3 and 30 mg/kg. Due to severe toxicity at 30 mg/kg, the dose level of Group 4 was adjusted to 10 mg/kg from Day 4 of the study onwards.

Males were exposed for 29 days, i.e. 2 weeks prior to mating, during mating, and up to termination. Females were exposed for 41-47 days, i.e. during 2 weeks prior to mating, during mating, during post-coitum, and during at least 4 days of lactation.

The following parameters were evaluated: mortality/viability, clinical signs, functional observations, body weights, food consumption, reproduction/developmental parameters, observations pups, clinical pathology (including thyroid hormones), macroscopy, organ weights,

and histopathology. Chemical analyses of formulations were conducted once during the study to assess accuracy, homogeneity and stability.

The following parameters were evaluated in the parental animals: mortality/viability, clinical signs, functional observations, body weights, food consumption, reproduction/developmental parameters, observations pups, clinical pathology (including thyroid hormones), macroscopy, organ weights, and histopathology. Pups were examined for viability, clinical signs, and body weights were determined. All pups were sexed and descriptions of all external abnormalities were recorded at necropsy. Chemical analyses of formulations were conducted once during the study to assess accuracy, homogeneity and stability.

No relevant parental toxicity was observed up to 10 mg/kg.

No reproduction/developmental toxicity was observed at any dose level. Based on these results, a reproduction and developmental No Observed Adverse Effect Level. (NOAEL) of 10 mg/kg was derived.

Based on the absence of functional or morphological disturbances supporting the changes noted for clinical biochemistry parameters, a parental NOAEL of 10 mg/kg was established.

Reference 2

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Published literature data

Qualifier:

no guideline followed

Principles of method if other than guideline:

Animals were randomly assigned to six groups of 15 animals each according to body weight and given different doses of iodine at the levels of 0, 1500, 3000, 6000, 12,000 and 24,000 µg/L by using sterile water as the vehicle. Four months later, female mice were placed into the metabolic cages of five mice each and urine samples over 3 h in the morning were collected for 3 days to measure urinary iodine concentration. Females were then paired overnight and examined for a vaginal plug the following morning. Dams were euthanized on day 19 of gestation.

GLP compliance:

no

Limit test:

no

Species:

mouse

Strain:

Balb/c

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Laboratory Animal Center of Hubei Provincial Center for Disease Control and Prevention (Wuhan, China)
- Age at study initiation: Not reported
- Weight at study initiation: Not reported
- Fasting period before study: No
- Diet (e.g. ad libitum): Ad libitum
- Water (e.g. ad libitum): Ad libitum
- Acclimation period: One week

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 2 ºC
- Humidity (%): Not reported
- Air changes (per hr): Not reported
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

oral: drinking water

Vehicle:

water

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: Not reported

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Iodine concentration in diet and water was measured by Cer-Arsenite colormetric method as modified by Fisher et al. (Anal Chem. 69:687-689, 1986).

Details on mating procedure:

- Impregnation procedure: cohoused
- If cohoused:
- M/F ratio per cage: 2 females: 1male
- Length of cohabitation: Overnight
- Further matings after two unsuccessful attempts: No
- Proof of pregnancy: vaginal plug referred to as [day 0 of pregnancy

Duration of treatment / exposure:

Animals were treated 4 months before and during gestation.

Frequency of treatment:

Daily (drinking water)

Duration of test:

Dams were euthanized on day 19 of gestation

Remarks:

Doses / Concentrations:
1,500 µg/L
Basis:
nominal in water

Remarks:

Doses / Concentrations:
3,000 µg/L
Basis:

Remarks:

Doses / Concentrations:
6,000 µg/L
Basis:
nominal in water

Remarks:

Doses / Concentrations:
12,000 µg/L
Basis:
nominal in water

Remarks:

Doses / Concentrations:
24,000 µg/L
Basis:
nominal in water

No. of animals per sex per dose:

10 female and 5 males per group

Control animals:

yes, concurrent no treatment

Details on study design:

- Dose selection rationale: Not reported, but presumibly necessary to obtain high iodine exposure.

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Daily


DETAILED CLINICAL OBSERVATIONS: No data


BODY WEIGHT: Yes
- Time schedule for examinations: Not reported

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): Yes
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No

WATER CONSUMPTION: Yes
- Time schedule for examinations: Statistic up to termination

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day # 19
- Organs examined:

OTHER: Urine samples over 3 h in the morning before mating to measure iodine to creatinine ratio. Thyroxine and triiodothyronine were also measured in day 19 of gestation. Histological examinaton of the thyroid was also performed as part of the maternal observations.

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes
Examinations included:
- gravid uterus weight: Yes
- Number of corpora lutea: No data
- Number of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: Yes
- Other:

Fetal examinations:

- External examinations: Yes:, all per litter
- Soft tissue examinations: Yes, all per litter
- Skeletal examinations: Yes, one-half to two-thirds per litter
- Head examinations: Yes, all per litter

Statistics:

Because of its skewed distribution, the median was used to describe the central tendency of urinary iodine concentration. The Kruskal–Wallis method was used to test the differences in ranking of urinary iodine concentration. One-way analysis of variance (ANOVA) was used to analyze thyroid hormone levels, maternal food and water consumption, maternal body weight gain, placental weight. Two-way ANOVA with factors = treatment and sex was performed to analysis the gender difference in fetal weight. When significant effects were observed by ANOVA, the data for the treated groups were compared statistically with the control group by Duncan’s multiple range test. The ratios of live, resorbed and dead fetuses were analyzed by variance and Duncan’s test after arcsine transformation. The incidence of skeletal anomalies was analyzed by χ2-test. Significance was set at the 0.05 probability level.

Indices:

Dams
Implants/litter

Fetuses
Live fetuses/implants
Resorbed fetuses/implants
Dead fetuses/implants
Ratio of males/total

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
Compared to control group, serum TT4 level increased and serum TT3 decreased significantly in dams when iodine dose reached 3000 µg/L.

Dose descriptor:

LOAEL

Effect level:

3 000 other: µg/L

Based on:

other: Test substance in drinking water

Basis for effect level:

other: developmental toxicity

Dose descriptor:

NOAEL

Effect level:

1 500 other: µg/L

Based on:

other: test substance in drinking water

Basis for effect level:

other: developmental toxicity

Dose descriptor:

NOAEL

Effect level:

1 500 other: µg/L

Based on:

other: Test substance in drinking water

Basis for effect level:

other: maternal toxicity

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:yes

Details on embryotoxic / teratogenic effects:
The results of fetal observation showed that high doses of iodine exposure induced a decrease in the incidence of live fetuses and an increase in the incidence of reabsorbed fetuses (Table 1). Excess iodine-associated reduction in fetal body weight was observed only in female fetuses of 6000, 12,000 or 24,000g/L groups. Neither obvious external alternations nor visceral malformations were found in fetuses in any treated groups.
Exposure to high doses of iodine resulted in an increase in the incidence of skeletal variations dose-dependently (r = 0.80, p < 0.05), and this increase was statistically significant in the high doses of iodine groups except 1500g/L group compared to control group (Table 2). Skeletal alterations included supernumerary ribs, agenesis of sternbrae, poor ossification of metacarpals and metatarsals, abnormal fusion of supraoccipital and malaligned vertebral centra. No multiple defects found in the same fetus. The form of ectopic or supernumerary ribs (SNR) was commonly observed (Table 2).

Dose descriptor:

LOAEL

Effect level:

1 500 other: µg/L

Based on:

other: test substance in drinking water

Basis for effect level:

other: fetotoxicity

Abnormalities:

not specified

Developmental effects observed:

not specified

Table 1: Pregnancy outcome following chronic high doses of iodine exposure.

Dose groups ( µg/L)	0	1500	3000	6000	12000	24000
Dams
Number of dams pregnant (%)	10 (100)	9 (90)	9 (90)	8 (80)	9 (90)	9 (90)
Number of examined litters	7	8	8	7	7	8
Implants/litter	5.6 ± 2.4	6.6 ± 1.3	7.3 ± 2.1	5.7 ± 1.3	7.6 ± 1.3	7.6 ± 1.5
Average daily food consumption (g)	4.8 ± 0.4	4.6 ± 0.3	4.7 ± 0.3	4.5 ± 0.5	4.3 ± 0.4*	4.3 ± 0.3
Average daily water consumption (mL)	4.9 ± 0.8	4.8 ± 0.9	4.8 ± 1.2	4.5 ± 1.3	4.2 ± 0.7	4.2 ± 1.2
Body weight gain (g)	11.386 ± 3.339	10.762 ± 2.058	11.363± 3.531	10.840 ± 1.705	11.243 ± 2.651	11.138 ± 3.673
Mean placenta weight (g)	0.126 ± 0.019	0.113 ± 0.014	0.106 ± 0.009*	0.104 ± 0.011*	0.109 ± 0.019*	0.102 ± 0.012*
Fetuses
Live fetuses/implants (%) (a)	92.3 ± 7.2	72.5 ± 9.4*	69.8 ± 14.6*	67.9 ± 17.5*	64.4 ± 10.0*	63.2 ± 17.4*
Resorbed fetuses/implants (%) (a)	7.7 ± 7.2	27.5 ± 9.4*	26.2 ± 10.8*	28.1 ± 13.5*	28.6 ± 13.1*	27.0 ± 15.3*
Dead fetuses/implants (%) (a)	0 ± 0	1.6 ± 4.4	4.1 ± 5.7	4.1 ± 7.0	7.0 ± 9.0	9.9 ± 15.1
Fetal body weight (g)
Males	1.21 ± 0.12	1.13 ± 0.29	1.14 ± 0.11	1.21 ± 0.12	1.21 ± 0.06	1.18 ± 0.11
Females	1.20 ± 0.13	1.09 ± 0.16	1.11 ± 0.11	1.05 ± 0.09*	1.05 ± 0.11*	1.05 ± 0.18*
Ratio of males/total	0.48	0.47	0.50	0.46	0.44	0.46

Data represented mean ± S.D.

(a) data were analyzed after arcsine transformation.

* p < 0.05 compared with the control group by χ2-test Table 2: Skeletal variations by chronic high doses of iodine exposure

Table 2: Skeletal variations by chronic high doses of iodine exposure

Dose groups ( µg/L)	0	1500	3000	6000	12000	24000
Dams
Number of examined litters	7	8	8	7	7	8
Number of fetuses examined (a)	22	23	19	18	22	28
Number of skeletal malformation (%) (b)	2 (9.1)	6 (26.1)	8 (42.1)*	8 (44.4) *	11 (50.0)*	15 (53.6)*
Supernumerary ribs	2	5	6	6	8	11
Agenesis of sternbrae	0	1	0	1	2	0
Poor ossification of metacarpals and metatarsals	0	0	0	0	0	1
Abnormal fusion of suppraoccipital	0	0	0	1	1	2
Malaligned vertebral centra	0	0	2	0	0	1

(a) One-half or two-thirds of the live fetuses were used for skeletal examination

(b) No multiple defects found in the same fetus

* p < 0.05 compared with the control group by χ2-test.

Conclusions:

Balb/C mice were given different doses of iodine at the levels of 0 (sterile water), 1500, 3000, 6000, 12,000 and 24,000 µg/L in drinking water for 4 months, then were mated and the developmental toxicity and teratogenicity were evaluated.

Serum total thyroxine (TT4) levels increased and serum total triiodothyronine (TT3) levels decreased significantly in dams when iodine dose reached 3000 µg/L. Maternal effect was evident by the reduction of average daily food consumption in higher doses of iodine groups. Embryotoxicity and teratogenicity were mainly indicated by the reduced body weight in female fetuses, the decreased number of live fetuses, and the increased incidence of resorptions, and especially skeletal variations.

Based on study results, embryotoxicity and teratogenicity were mainly indicated by the reduced body weight in female fetuses, the decreased number of live fetuses, and the increased incidence of resorptions, and especially skeletal variations. A NOAEL for fetotoxicity could not be obtained. Fetotoxicity LOAEL was 1500 µg/L.

Executive summary:

To evaluate the effects of chronic exposure to high amounts of iodine on pregnancy and fetal outcome, Balb/C mice were given different doses of iodine at the levels of 0, 1500, 3000, 6000, 12,000 and 24,000 µg/L by using sterile water as the vehicle. Four months later, female mice were placed into the metabolic cages of five mice each and urine samples over 3 h in the morning were collected for 3 days to measure urinary iodine concentration. Females were then paired overnight and examined for a vaginal plug the following morning. Dams were euthanized on day 19 of gestation. Animals were examined daily and after euthanization thyroid was examined as well as thyroidal hormones levels were measured. The gravid uterus of the pregnant mice were weighed, the number of positions of the live or dead fetuses, together with resorptions, were recorded. Live fetuses were examined for external abnormalities and for skeletal examination.

 

An obvious colloid goiter was observed, and serum total thyroxine (TT4) levels increased, and serum total triiodothyronine (TT3) levels decreased significantly in dams when iodine dose reached 3000 µg/L . Maternal effect was evident by the reduction of average daily food consumption in higher doses of iodine groups. Embryotoxicity and teratogenicity were mainly indicated by the reduced body weight in female fetuses, the decreased number of live fetuses, and the increased incidence of resorptions, and especially skeletal variations.

 

Specifically, high doses of iodine exposure induced a decrease in the incidence of live fetuses and an increase in the incidence of reabsorbed fetuses. Excess iodine-associated reduction in fetal body weight was observed only in female fetuses of 6000, 12,000 or 24,000g/L groups. Neither obvious external alternations nor visceral malformations were found in fetuses in any treated groups. Exposure to high doses of iodine resulted in an increase in the incidence of skeletal variations dose-dependently and this increase was statistically significant in the high doses of iodine groups except 1500g/L group compared to control group. Skeletal alterations included supernumerary ribs, agenesis of sternbrae, poor ossification of metacarpals and metatarsals, abnormal fusion of supraoccipital and malaligned vertebral centra. No multiple defects found in the same fetus. The form of ectopic or supernumerary ribs (SNR) was commonly observed (Table 2).

 

Based on study results, embryotoxicity and teratogenicity were mainly indicated by the reduced body weight in female fetuses, the decreased number of live fetuses, and the increased incidence of resorptions, and especially skeletal variations. A NOAEL for fetotoxicity could not be obtained. Fetotoxicity LOAEL was 1500 µg/L.

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

10 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Quality of whole database:

Animal data available including an OCD 422 study identified as the key study. Human data available from expert opinions, thes data ar described below, and further in section 7.10.

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Additional information

Other animal data reported in section 7.8.2 but considered less relevant:

In the following, a number of the most relevant supportive animal data are described:

- Vorhees CV (1984) showed that Potassium iodide (KI) when fed to male and female rats before and during breeding, to females only during gestation and lactation, and to their offspring after weaning (day 21 after birth) through to day 90, at levels of 0, 0.025, 0.05 or 0.1% (w/w) of the diet (approx. 20, 40, 90 mg/kg bw/day, respectively showed evidence of developmental toxicity at doses of up to 0.1% in the diet (90 mg/kg bw/day).

- Zhang (2012) shoved that when female Wistar rats was maintained on low-iodine grain assigned to three groups based on iodated water concentration: low iodine (LI, 1.2 μg/d), normal iodine (NI, 5–6 μg/d), and 3-fold high iodine (3HI, 15–16 μg/d), both low and high levels of iodine intake by rats could affect the neurological development of offspring. Specifically, the neurodevelopmental and cognitive deficits of the 3HI pups were mild and temporary, likely related to the changes in hippocampal protein expressions of BDNF and NSP-A.

- Saghir (2012) showed that the biocide diiodomethyl-p-tolylsulfone (DIMPTS) caused dystocia, decreased neonatal survival and hypothyroidism in rat reproduction studies, resembling the effects caused by iodine. One molecule of DIMPTS contains two iodine moieties that are hydrolysed upon ingestion and systemically absorbed, suggesting iodine toxicity as a probable mode of action for the effects observed in rats.

- Caroline (2017) investigated the impact of iodine excess (lE) exposure during pregnancy and lactation periods on maternal hypothalamus-pituitary-thyroid axis in rats. One group of dams was supplied with distilled water supplemented with 0.6 mg/L NaI during pregnancy and lactation periods (Iodine 0.6 mg/L) and another group of dams was supplied with distilled water supplemented with 7.3 mg/L Nal during pregnancy and lactation periods (7.3 mg/L). The study showed that exposure to IE during pregnancy and lactation induces primary hypothyroidism in rat dams and impairs iodide transfer to the milk.

Human data (from expert opinions):

The teratogenic/developmental effects secondary to excess and deficiency of iodine in humans subjects are well known from literature data. Human case reports show that highly excessive intake of iodine (lowest reported dose 130 mg/day) during pregnancy may result in neonatal goitre/hypertrophy (WHO, 2009). This could be explained by the fact that excess iodine is transferred via the placenta resulting in the fetal exposure to iodine overload (Sun and Yang, 2009).

 

The US Agency for Toxic Substances and Disease Register (2004) has reviewed in extent the information available on developmental effects of iodine:

"Exposure to excess stable iodine may produce hypothyroidism and hyperthyroidism, which could give rise to developmental defects secondary to thyroid gland dysfunction (Boyages 2000a, 2000b). Hypothyroidism may be associated with impairment in neurological development of the fetus or growth retardation (Boyages 2000a, 2000b; Snyder 2000a). Martin and Rento (1962) reported two cases of goiter and severe transient hypothyroidism, without neurological sequellae in infants born to mothers who ingested potassium iodide during pregnancy; the approximate dosages were 920 and 1,530 mg I/day (13 and 22 mg/kg/day). Growth acceleration may occur in childhood hyperthyroidism, which is thought to be related to accelerated pituitary growth hormone turnover or a direct effect of thyroid hormone on bone maturation and growth (Snyder 2000b). Although iodine excess may result in hypothyroidism, iodine deficiency is far more likely to cause prenatal and postnatal hypothyroidism and be associated with neurologic injury leading to cretinism, a developmental effect. Thyroid hormone deficiency from any cause at critical times of development may result in severe mental retardation, neurologic abnormalities, growth retardation, or abnormal pubertal development."

WHO (2020) also discusses effects of iodine on human reproduction with the follwing observations:

 "Exposure to iodine may give rise to developmental defects, as a result of thyroid gland dysfunction (Boyages, 2000a,b). Hypothyroidism may be associated with impairment in neurological development of the fetus, as noted above, or growth retardation (Boyages, 2000a,b; Snyder, 2000a; Krassas, Poppe & Glinoer, 2010).Hyperthyroidism in humans was associated with accelerated growth linked to accelerated pituitary growth hormone turnover or a direct effect of thyroid hormone on bone maturation and growth (Snyder, 2000b)".

As human data is available, data on experimental animals are considered secondary to human data in relation to the assessment of effets to fertility and development.

 

Key references:

- Agency for Toxic Substances and Disease Registry (ATSDR). 2004. Toxicological profile for iodine.

- World Health Organization (WHO). 2009. Iodine and inorganic iodides. In: Concise International Chemical Assessment Document 72.

- WHO, 2020: Iodin in drinking water, Background document for development of WHO guidelines for drinking-water quality.

Toxicity to reproduction: other studies

Additional information

The thyroid gland is the main storage organ for iodine. It is also the target of iodine toxicity and impairment of the thyroid homeostasis/thyroid hormone levels can lead to differnt conditions - hypothyroidism (with or without goitre – enlargement of the thyroid), hyperthyroidism, and changes in the incidence and types of thyroid malignancies.

Available animal and human data shows that both iodine deficiency as well as excess iodine can impair thyroid homeostasis/thyroid hormone levels with potential to impact on the thyroid homone metabolism and potentially also the thyroid - pituitary axis and therfore also neurological effects. This is particularly applicable to fetuses and newborn infants, because thyroid hormones are essential to the development of the neuromuscular system and brain. An iodine-induced hypothyroid state can result in delayed or deficient development of the brain and neuromuscular system of the newborn (WHO, 2020).

The impairment of the thyroid homeostasis/thyroid hormone levels and the following deswcirbe conditions can be considered as an endocrine effect. But as iodine is a physiologically essential element, the consept of endocrine disruption is not meaningfull. This is also the conclusion from the registration dossier of iodine (including PVP-iodine) as an active substance for biocidal products (Ref: Assessment report, Iodine (including PVP-iodine) Product types 1, 3, 4, 22, 13 December 2013, Sweden) as referenced below:

"Iodine is an essential element and has a physiological function in thyroid hormone synthesis (i.e. intentionally interacts with the endocrine system). This means that both iodine deficiency as well as excess iodine can impair thyroid homeostasis/thyroid hormone levels. This is to be considered as an endocrine effect. However, it would not be justified to conclude from this that iodine should be considered to be an endocrine disruptor. In contrast to typical xenobiotic substances, which are not needed at all for the functioning of the human body, and which normally only have negative effects on man, Iodine is a physiologically essential element.Consequently, the concept of endocrine disruption is not meaningful for essential elements such as iodine since it neglects that they are needed for maintaining hormone homeostasis.Furthermore, neither iodine nor iodide are included in the lists of the EU on substances suspected of interfering with the hormone systems of humans and wild-life".

Mode of Action Analysis / Human Relevance Framework

The mechanism by which excess iodide produces hypothyroidism is not completely understood. It has been proposed that excess iodide inhibits the iodination of thyroglobulin in the thyroid gland, and inhibits the release of T4 and T3 from the gland. As a consequence, TSH release is stimulated, leading to increased serum levels. Hypertrophy of the thyroid gland is an additional potential effect that is known to accompany iodide-induced suppression of the thyroid gland (WHO, 2020).

Justification for classification or non-classification

When assessng the relevance of classification for fertility and development the following has to be considered:

The impairment of the thyroid homeostasis/thyroid hormone levels and the following deswcirbe conditions can be considered as an endocrine effect. But as iodine is a physiologically essential element, the consept of endocrine disruption is not meaningfull. This is also the conclusion from the registration dossier of iodine (including PVP-iodine) as an active substance for biocidal products (Ref: Assessment report, Iodine (including PVP-iodine) Product types 1, 3, 4, 22, 13 December 2013, Sweden) as referenced below:

"Iodine is an essential element and has a physiological function in thyroid hormone synthesis (i.e. intentionally interacts with the endocrine system). This means that both iodine deficiency as well as excess iodine can impair thyroid homeostasis/thyroid hormone levels. This is to be considered as an endocrine effect. However, it would not be justified to conclude from this that iodine should be considered to be an endocrine disruptor. In contrast to typical xenobiotic substances, which are not needed at all for the functioning of the human body, and which normally only have negative effects on man, Iodine is a physiologically essential element.Consequently, the concept of endocrine disruption is not meaningful for essential elements such as iodine since it neglects that they are needed for maintaining hormone homeostasis.Furthermore, neither iodine nor iodide are included in the lists of the EU on substances suspected of interfering with the hormone systems of humans and wild-life".

A similar argumentation can be applied regarding clssification for reproductive toxicity:

The effects of iodine on human reproduction are well known from literature data. Iodine is an essential nutritional dietary element, it is required for the synthesis of the thyroid hormones, which control metabolism and play an important role in reproduction, growth and development. Exposure to excess iodine may produce hypothyroidism or hyperthyroidism and could cause endocrine effects and disruption of reproductive function, secondary to thyroid gland dysfunction. Effects on fertility and developmental are therefore considered as secondary effects to thyroid impairment and as classification with STOT RE1 H372 (thyroid) applies for iodine, no classification according to Regulation (EC) No 1271/2008 for the secondary effects on reproduction and development is warranted.